The goal of this work is to understand, at the molecular level, the mechanisms of mother cell specific transcriptional regulation in Saccharomyces cerevisiae. The yeast HO gene is transcribed only in mother cells, one of the two cell types of cells descending from each mitotic division. An analogy can be drawn between this lineage specificity in HO expression and the differential gene regulation which occurs during embryonic development. Two proteins, SWI5 and SDI1, have been identified which bind to the HO promoter and are also involved in determining the mother cell specificity of HO gene expression. The interactions of these proteins with DNA and with each other will be characterized in detail. This information will be used to develop specific models of transcriptional regulation, and these models will be tested by in vitro and in vivo experiments. Additional genes regulated by SWI5 and SDI1 will be cloned from the yeast genome. The regulatory properties of these genes will be determined, and the promoters will be characterized for DNA sites recognized by these two site-specific DNA-binding proteins. Further information on the mechanism of mother cell specific transcription will be available by comparing these genes with HO, specifically by analyzing their protein-DNA interactions and their transcriptional regulation.